Magnesium oxide (CAS NO.1309-48-4) has many uses:1.In medicine, it is used for relief for heartburn and sore stomach, as an antacid, magnesium supplement, and as a short-term laxative. It is also used to improve symptoms of indigestion. Side effects of magnesium oxide may include nausea and cramping.In quantities sufficient to obtain a laxative effect, side effects of long-term use include enteroliths resulting in bowel obstruction. 2.It is used extensively in electrical heating as a component of "CalRod"-styled heating elements. There are several mesh sizes available and most commonly used ones are 40 and 80 mesh per the American Foundry Society. The extensive use is due to its high dielectric strength and average thermal conductivity. MgO is usually crushed and compacted with minimal airgaps or voids. The electrical heating industry also experimented with aluminium oxide, but it is not used anymore. 3.It is used as a reference white color in colorimetry, owing to its good diffusing and reflectivity properties.It may be smoked onto the surface of an opaque material to form an integrating sphere. 4.It is used as a principal ingredient in construction materials used for fireproofing. 5.It is used by many libraries for preserving books by reacting with ambient moisture to dry the book storage areas. 6.Used as a basic refractory material for crucibles. 7.Used as an insulator in industrial cables.